Lara had some money. She spent one pound 25 on a drink and one pound 60 on a sandwich. She has three-quarters of her money left. How much money did Lara have to start with?
We know she spent one pound 25 on a drink and one pound 60 on a sandwich. One pound 25 plus one pound 60 equals two pounds 85. We also know that Lara has three quarters of her money left. This means that two pound 85 is a quarter of her money. So if we multiply two pound 85 by four, this will tell us how much money Lara had to start with.
Multiplying by four is the same as doubling and doubling again. So double two pounds 85 or two pounds 85 multiplied by two. Two times two pounds is four pounds. And two times 85 is 170, as 170 pence which is one pound 70. Four pounds and one pound 70 makes five pounds 70. Now we can double again. Five pounds 70 times two, two times five pounds is 10 pounds and two times 70 is 140 pence or one pound 40. 10 pounds and one pound 40 is 11 pounds 40. Two pounds 85 multiplied by four is 11 pounds 40.
So Lara had 11 pounds 40 to start with. First, we added together the amount Lara had already spent which was two pounds 85. As this was a quarter of the money which Lara had to begin with, we multiplied two pounds 85 by four, which gave us our answer, 11 pounds 40.